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Why are my 3 y/o SunPower panels only outputting 66%?

manly

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Jun 23, 2021
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I have Qty (3) 320 watt rigid SunPower panels on a boat I recently bought:


These are only 3 years old. Spec sheets rates them 90% output at 12 years. In full sun yesterday (angled a bit towards the sun which is lower this time of year in Florida) I was only getting 640 watts.

Going through Victron charge controllers. What gives? Is the sun just as not as powerful in the winter? Perhaps the wire is undersized? Is this normal?

Any input would be appreciated.
 
What is the highest output they have generated in the past? Also bear in mind that when batteries are being topped off at the high end of charging profile, your solar controller will limit the amount of charge going to them. Did you check at best position angle of sun, 90 degrees of sun to the panel? When the batteries were 60 percent or less of charge? Just fyi, due to angle of sun in the winter, I am lucky to get 600 watts out of 4 panels that should be putting out 1220 watts. What size of wire do you have coming from your panels to your controller?
 
Thank you the reply GLC.

What is the highest output they have generated in the past?
Good idea. Looking thru Victorn history, the highest was 677 watts 29 days ago. 677/960 is 71% of rated output.

Did you check at best position angle of sun, 90 degrees of sun to the panel?
The panels array is fixed at a slight angle and never exactly facing the sun. Probably about 20 degrees off at best.

Where the batteries 60 percent or less of charge?
Yeah, about 65%, so charging in bulk mode.

What size of wire do you have coming from your panels to your controller?
10 awg. Two sets of conductors, one with 640 watts (two 320 watts in parallel) and the other 320 watts by itself. The run is about 10' long to the charge controllers. Less than 1% voltage drop.


Maybe my problem is mainly the position of the sun angle. I'll just keep an eye on them throughout this next summer and see if I get better results.
 
Yes position of sun compared to the panels makes a big difference. Also like i said above, mine have never put out as advertised watts. I have never heard of any doing it. During the year, with best sun angle, I have only collected 960watts out of the 1220 watts advertised. Just sayin.
 
At 38 deg lat. 1600W pv array angle at 53 deg above horizon (winter setting), 1050W is the max I’m seeing right now on a perfect, dry winter day (ha- one or two days per month).
 
To really measure the real-time output of your panels accurately, you need to apply a load to your system that is as large or somewhat larger than the combined output of the string.

So, for three 320W panels you need to apply a load in the range of 960W. A toaster would work well here. Do this test when the panels are oriented exactly at the sun sometime around noon with a battery that is close to fully charged.
 
We are a week past winter solstice. Even in S. Florida the sun's maximum angle above south horizon is now 40 degrees. Do you have previous winter's output for reference?

There are a lot of other things in a given system that can also degrade output. On a boat, just the shadow of an overhead rope can hurt a lot.
 
@RCinFLA, I'm thinking the sun angle must be the biggest issue.

If sun is getting to ~40 degrees in the sky and my panels appear to be angled 5 degrees or so, that means sun is hitting 45 degrees best case scenario.

I attached a picture of the solar installation (done by previous owner). Almost makes me think it would be worth the fuss to make the panel angles adjustable. But that adds complexity. Petty simple design now.

Just pulled the trigger on ordering 960 watts of Rich Solar CIGS. That was 3 boat bucks. Plus charge controllers and wires makes it closer to 4 boat bucks. These will go on top my cockpick enclosure. Curious to see how those work out.

p.s. Handy sun chart I found for Florida: http://www.fsec.ucf.edu/en/publications/pdf/fsec-dn-4-83.pdf

p.p.s. Seems like you have the angle dialed in pretty well @RV10flyer, and still getting 65% output. Wonder if the sunlight just isn't as powerful in wintertime somehow, even if the panels are pointed right to the sun? Perhaps since light is passing through more atmosphere, some of the power gets absorbed there.

20211231_122714.jpg
 
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I just lashed up 4 Kyocera 235W panels in my back yard to play with. I guess they are about 10 years old. 2s2p mode I am getting around 900W out of them, so well within their ratings. I got an extra 1.3 volts by cleaning them !!!
 
Great, was that with a controller and battery charging or no batteries?
 
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